1. Field of the Invention
The present invention relates to a semiconductor device which includes, as a circuit, a thin film transistor (hereinafter referred to as TFT) using a semiconductor thin film, and a technique regarding a method of manufacturing the same. Incidentally, in the present specification, the semiconductor device means any device which is made to function by using a semiconductor.
Thus, the term “semiconductor device” recited throughout this specification includes not only a single semiconductor component such as a TFT, but also an electro-optical device with TFTs, a semiconductor circuit, and an electronic equipment having those.
2. Description of the Related Art
In recent years, a TFT used for an electro-optical device such as an active matrix type liquid crystal display device has been actively developed. The active matrix type liquid crystal display device is a monolithic display device in which a pixel matrix circuit and a driver circuit are provided on the same substrate.
Moreover, recently, an experiment of forming a semiconductor circuit having a function comparable to a conventional IC by using TFTs provided on a substrate has also been made. For example, the development of a system-on-panel having a built-in logic circuit such as a γ-correction circuit, a memory circuit, and a clock generating circuit has been under review.
Since such a driver circuit or a logic circuit is required to perform a high speed operation, it is unsuitable to use an amorphous semiconductor film (typically, an amorphous silicon film) as an active layer. Thus, under the present circumstances, a crystalline semiconductor film (typically, a polysilicon film) has been examined.
However, when circuit performance comparable to a conventional IC comes to be required for a circuit assembled with TFTs, such circumstances have occurred that it is difficult to manufacture a TFT having satisfactory performance to meet the circuit specification by using a crystalline semiconductor film formed through a conventional technique.